An RGD-Containing Peptide Derived from Wild Silkworm Silk Fibroin Promotes Cell Adhesion and Spreading

Protein-based nanoparticles for therapeutic nucleic acid delivery

To realize the full potential of emerging nucleic acid therapies, there is a need for effective delivery agents to transport cargo to cells of interest. Protein materials exhibit several unique properties, including biodegradability, biocompatibility, ease of functionalization via recombinant and chemical modifications, among other features, which establish a promising basis for therapeutic nucleic acid delivery systems. In this review, we highlight progress made in the use of non-viral protein-based nanoparticles for nucleic acid delivery in vitro and in vivo, while elaborating on key physicochemical properties that have enabled the use of these materials for nanoparticle formulation and drug delivery. To conclude, we comment on the prospects and unresolved challenges associated with the translation of protein-based nucleic acid delivery systems for therapeutic applications.

The integration of peri-implant soft tissues around zirconia abutments: Challenges and strategies

Stable soft tissue integration around the implant abutment attenuates pathogen penetration, protects underlying bone tissue, prevents peri-implantitis and is essential in maintaining long-term implant stability. The desire for "metal free" and "aesthetic restoration" has favored zirconia over titanium abutments, especially for implant restorations in the anterior region and for patients with thin gingival biotype. Soft tissue attachment to the zirconia abutment surface remains a challenge. A comprehensive review of advances in zirconia surface treatment (micro-design) and structural design (macro-design) affecting soft tissue attachment is presented and strategies and research directions are discussed. Soft tissue models for abutment research are described. Guidelines for development of zirconia abutment surfaces that promote soft tissue integration and evidence-based references to inform clinical choice of abutment structure and postoperative maintenance are presented.

Comparison of NIH 3T3 Cellular Adhesion on Fibrous Scaffolds Constructed from Natural and Synthetic Polymers

Polymer scaffolds are increasingly ubiquitous in the field of tissue engineering in improving the repair and regeneration of damaged tissue. Natural polymers exhibit better cellular adhesion and proliferation than biodegradable synthetics but exhibit inferior mechanical properties, among other disadvantages. Synthetic polymers are highly tunable but lack key binding motifs that are present in natural polymers. Using collagen and poly(lactic acid) (PLA) as models for natural and synthetic polymers, respectively, an evaluation of the cellular response of embryonic mouse fibroblasts (NIH 3T3 line) to the different polymer types was conducted. The samples were analyzed using LIVE/DEAD™, alamarBlue™, and phalloidin staining to compare cell proliferation on, interaction with, and adhesion to the scaffolds. The results indicated that NIH3T3 cells prefer collagen-based scaffolds. PLA samples had adhesion at the initial seeding but failed to sustain long-term adhesion, indicating an unsuitable microenvironment. Structural differences between collagen and PLA are responsible for this difference. Incorporating cellular binding mechanisms (i.e., peptide motifs) utilized by natural polymers into biodegradable synthetics offers a promising direction for biomaterials to become biomimetic by combining the advantages of synthetic and natural polymers while minimizing their disadvantages.

Immobilization of Arg-Gly-Asp peptides on silk fibroin via Gly-Ala-Gly-Ala-Gly-Ser sequences

A simple method by which the functional peptide of Gly-Arg-Gly-Asp-Ser (GRGDS) is immobilized on the surface of silk fibroin (SF) films via Gly-Ala-Gly-Ala-Gly-Ser (GAGAGS) sequences is proposed. GAGAGS, a repeating amino acid sequence in the crystal region of Bombyx mori SF, performs a key role in interacting with and immobilizing SF molecules. Immobilization by this proposed method involves no chemical reaction, thereby preserving the original properties of the SF molecule. The density of GRGDS peptides existing on SF film was found to be higher in the GAGAGS-bound type than in the non-GAGAGS-bound type. Furthermore, results showed that the amount of immobilized (GAGAGS)GRGDS peptide increased as the β-sheet crystallization was promoted in the SF film. Fibroblasts, which adhered to the surface of the SF film, showed more extensibility because of the (GAGAGS)GRGDS immobilization, which suggests that the cell adhesion activity of RGD is functioning effectively.

Biodegradable and biocompatible synthetic polymers for applications in bone and muscle tissue engineering

In medicine, tissue engineering has made significant advances. Using tissue engineering techniques, transplant treatments result in less donor site morbidity and need fewer surgeries overall. It is now possible to create cell-supporting scaffolds that degrade as new tissue grows on them, replacing them until complete body function is restored. Synthetic polymers have been a significant area of study for biodegradable scaffolds due to their ability to provide customizable biodegradable and mechanical features as well as a low immunogenic effect due to biocompatibility. The food and drug administration has given the biodegradable polymers widespread approval after they showed their reliability. In the context of tissue engineering, this paper aims to deliver an overview of the area of biodegradable and biocompatible synthetic polymers. Frequently used synthetic biodegradable polymers utilized in tissue scaffolding, scaffold specifications, polymer synthesis, degradation factors, as well as fabrication methods are discussed. In order to emphasize the many desired properties and corresponding needs for skeletal muscle and bone, particular examples of synthetic polymer scaffolds are investigated. Increased biocompatibility, functionality and clinical applications will be made possible by further studies into novel polymer and scaffold fabrication approaches.  

Current advances in cell therapeutics: A biomacromolecules application perspective

INTRODUCTION

Many chronic diseases have evolved and to circumvent the limitations of using conventional drug therapies, smart cell encapsulating delivery systems have been explored to customize the treatment with alignment to disease longevity. Cell therapeutics has advanced in tandem with improvements in biomaterials that can suitably deliver therapeutic cells to achieve targeted therapy. Among the promising biomacromolecules for cell delivery are those that share bio-relevant architecture with the extracellular matrix and display extraordinary compatibility in the presence of therapeutic cells. Interestingly, many biomacromolecules that fulfil these tenets occur naturally and can form hydrogels.

AREAS COVERED

This review provides a concise incursion into the paradigm shift to cell therapeutics using biomacromolecules. Advances in the design and use of biomacromolecules to assemble smart therapeutic cell carriers is discussed in light of their pivotal role in enhancing cell encapsulation and delivery. In addition, the principles that govern the application of cell therapeutics in diabetes, neuronal disorders, cancers and cardiovascular disease are outlined.

EXPERT OPINION

Cell therapeutics promises to revolutionize the treatment of various secretory cell dysfunctions. Current and future advances in designing functional biomacromolecules will be critical to ensure that optimal delivery of therapeutic cells is achieved with desired biosafety and potency.

Electrophoretic deposition of silk fibroin coatings with pre-defined architecture to facilitate precise control over drug delivery

The therapeutic precision and clinical applicability of drug-eluting coatings can be substantially improved by facilitating tunable drug delivery. However, the design of coatings which allows for precise control over drug release kinetics is still a major challenge. Here, a double-layered silk fibroin (SF) coating system was constructed by sequential electrophoretic deposition. A mixture of dissolved Bombyx mori SF (bmSF) molecules and pre-made bmSF nanospheres at different ratios was deposited as under-layer. Subsequently, this underlayer was covered by a top-layer comprising Antheraea pernyi SF (apSF) molecules (rich in arginylglycylaspartic acid, RGD) to improve the cellular response of the resulting double-layered coatings. Additionally, model drug doxycycline was either pre-mixed with dissolved bmSF molecules or pre-loaded into pre-made bmSF nanospheres at the same amount before their mixing and deposition. The thickness and nanosphere content of the under-layer architecture were proportional to the deposition time and nanosphere concentration in precursor mixtures, respectively. The surface topography, wettability, degradation rate and adhesion strength were comparable within the double-layered coating system. As expected, RGD-rich apSF top-layer improved cell adhesion, spreading and proliferation compared with bmSF top-layer. Furthermore, the amount and duration of drug release increased linearly with increasing nanosphere concentration at fixed deposition time, whereas drug release amount increased linearly with increasing deposition time. These results indicate that the dosage and kinetics of loaded drugs can be quantitatively tailored by altering nanosphere concentration and deposition time as main processing parameters. Overall, this study illustrates the strong potential of pre-defining coating architecture to facilitate control over drug delivery.

Immune Response to Silk Sericin-Fibroin Composites: Potential Immunogenic Elements and Alternatives for Immunomodulation

The unique properties of silk proteins (SPs), particularly silk sericin (SS) and silk fibroin (SF), have attracted attention in the design of scaffolds for tissue engineering over the past decades. Since SF has good mechanical properties, while SS displays bioactivity, scaffolds combining both proteins should exhibit complementary properties enhancing the potential of these materials. Unfortunately, SS-SF composites can generate chronic immune responses and their immunogenic element is not completely clear. The potential of SS-SF composites in tissue engineering, elements which may contribute to their immunogenicity, and alternatives for their preparation and design, to modulate the immune response and take advantage of their useful properties, are discussed in this review. It is known that SS can enhance β-sheet formation in SF, which may act as hydrophobic regions with a strong affinity for adsorption proteins inducing the chronic recruitment of inflammatory cells. Therefore, tailoring the exposure of hydrophobic regions at the scaffold surface should represent a viable strategy to modulate the immune response. This can be achieved by coating SS-SF composites with SS or other hydrophilic polymers, to take advantage of their antibiofouling properties. Research is still needed to realize the full potential of these composites for tissue engineering.

Micropatterned Silk-Fibroin/Eumelanin Composite Films for Bioelectronic Applications

There has been growing interest in the use of natural bionanomaterials and nanostructured systems for diverse biomedical applications. Such materials can confer unique functional properties as well as address concerns pertaining to sustainability in production. In this work, we propose the biofabrication of micropatterned silk fibroin/eumelanin composite thin films to be used in electroactive and bioactive applications in bioelectronics and biomedical engineering. Eumelanin is the most common form of melanin, naturally derived from the ink of cuttlefish, having antioxidant and electroactive properties. Another natural biomaterial, the protein silk fibroin, is modified with photoreactive chemical groups, which allows the formation of electroactive eumelanin thin films with different microstructures. The silk fibroin/eumelanin composites are fabricated to obtain thin films as well as electroactive microstructures using UV curing. Here, we report for the first time the preparation, characterization, and physical, electrochemical, and biological properties of these natural silk fibroin/eumelanin composite films. Higher concentrations of eumelanin incorporated into the films exhibit a higher charge storage capacity and good electroactivity even after 100 redox cycles. In addition, the microscale structure and the cellular activity of the fibroin/eumelanin films are assessed for understanding of the biological properties of the composite. The developed micropatterned fibroin/eumelanin films can be applied as natural electroactive substrates for bioapplications (e.g., bioelectronics, sensing, and theranostics) because of their biocompatible properties.

Silk Fibroin: An Ancient Material for Repairing the Injured Nervous System

Silk refers to a family of natural fibers spun by several species of invertebrates such as spiders and silkworms. In particular, silkworm silk, the silk spun by Bombyx mori larvae, has been primarily used in the textile industry and in clinical settings as a main component of sutures for tissue repairing and wound ligation. The biocompatibility, remarkable mechanical performance, controllable degradation, and the possibility of producing silk-based materials in several formats, have laid the basic principles that have triggered and extended the use of this material in regenerative medicine. The field of neural soft tissue engineering is not an exception, as it has taken advantage of the properties of silk to promote neuronal growth and nerve guidance. In addition, silk has notable intrinsic properties and the by-products derived from its degradation show anti-inflammatory and antioxidant properties. Finally, this material can be employed for the controlled release of factors and drugs, as well as for the encapsulation and implantation of exogenous stem and progenitor cells with therapeutic capacity. In this article, we review the state of the art on manufacturing methodologies and properties of fiber-based and non-fiber-based formats, as well as the application of silk-based biomaterials to neuroprotect and regenerate the damaged nervous system. We review previous studies that strategically have used silk to enhance therapeutics dealing with highly prevalent central and peripheral disorders such as stroke, Alzheimer's disease, Parkinson's disease, and peripheral trauma. Finally, we discuss previous research focused on the modification of this biomaterial, through biofunctionalization techniques and/or the creation of novel composite formulations, that aim to transform silk, beyond its natural performance, into more efficient silk-based-polymers towards the clinical arena of neuroprotection and regeneration in nervous system diseases.

Composition and in silico structural analysis of fibroin from liquid silk of non-mulberry silkworm Antheraea assamensis

Silk is spun from the liquid precursor known as liquid silk secreted from the posterior part and stored in the silk gland lumen with occurrence of many momentary events. The liquid silk in the silk gland is transformed to the spun silk fibre. In this study the elucidation of the protein components of liquid silk from the posterior part of the silk gland (PSG) of saturniid silkworm Antheraea assamensis along with its structural characterization has been reported. The 3D model of the N-terminal amorphous portion with some repeat crystalline motifs (19-255) of core protein fibroin has also been constructed. 1D and 2D electrophoresis revealed the homo-dimeric structure of the silk protein. Secondary structure analysis by Circular dichroism, FTIR spectroscopy showed α helical structural component as predominant conformation in the liquid silk. The crystalline structure investigated through X ray diffraction (XRD) analysis also revealed the presence of less ordered amorphous α helical conformation in the liquid silk. The 3D structural model proposed of the residues from 19 to 255 has revealed structural stability throughout the molecular dynamics simulation process. This study will provide the detailed structural information and in silico analysis of the core protein present in the liquid silk of PSG.

Silk fibroin nanoscaffolds for neural tissue engineering

The nervous system is a crucial component of the body and damages to this system, either by injury or disease, can result in serious or potentially lethal consequences. An important problem in neural engineering is how we can stimulate the regeneration of damaged nervous tissue given its complex physiology and limited regenerative capacity. To regenerate damaged nervous tissue, this study electrospun three-dimensional nanoscaffolds (3DNSs) from a biomaterial blend of silk fibroin (SF), polyethylene glycol (PEG), and polyvinyl alcohol (PVA). The 3DNSs were characterised to ascertain their potential suitability for direct implant into the CNS. The biological activity of 3DNSs was investigated in vitro using PC12 cells and their effects on reactive astrogliosis were assessed in vivo using a photothrombotic model of ischaemic stroke in mice. Results showed that the concentration of SF directly affected the mechanical characteristics and internal structure of the 3DNSs, with formulations presenting as either a gel-like structure (SF ≥ 50%) or a nanofibrous structure (SF ≤ 40%). In vitro assessment revealed increased cell viability in the presence of the 3DNSs and in vivo assessment resulted in a significant decrease in glial fibrillary acidic protein (GFAP) expression in the peri-infarct region (p < 0.001 for F2 and p < 0.05 for F4) after stroke, suggesting that 3DNSs could be suppressing reactive astrogliosis. The findings enhanced our understanding of physiochemical interactions between SF, PEG, and PVA, and elucidated the potential of 3DNSs as a potential therapeutic approach to stroke recovery, especially if these are used in conjunction with drug or cell treatment.

Bioinspired Materials for Wound Healing Application: The Potential of Silk Fibroin

Nature is an incredible source of inspiration for scientific research due to the multiple examples of sophisticated structures and architectures which have evolved for billions of years in different environments. Numerous biomaterials have evolved toward high level functions and performances, which can be exploited for designing novel biomedical devices. Naturally derived biopolymers, in particular, offer a wide range of chances to design appropriate substrates for tissue regeneration and wound healing applications. Wound management still represents a challenging field which requires continuous efforts in scientific research for definition of novel approaches to facilitate and promote wound healing and tissue regeneration, particularly where the conventional therapies fail. Moreover, big concerns associated to the risk of wound infections and antibiotic resistance have stimulated the scientific research toward the definition of products with simultaneous regenerative and antimicrobial properties. Among the bioinspired materials for wound healing, this review focuses attention on a protein derived from the silkworm cocoon, namely silk fibroin, which is characterized by incredible biological features and wound healing capability. As demonstrated by the increasing number of publications, today fibroin has received great attention for providing valuable options for fabrication of biomedical devices and products for tissue engineering. In combination with antimicrobial agents, particularly with silver nanoparticles, fibroin also allows the development of products with improved wound healing and antibacterial properties. This review aims at providing the reader with a comprehensive analysis of the most recent findings on silk fibroin, presenting studies and results demonstrating its effective role in wound healing and its great potential for wound healing applications.